This application claims the priority of German Patent Document 100 47 200.1, filed Sep. 23, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a starter device, predominantly for cold-starting, for fuel cell systems. The fuel cell system including a current generation system for generating electrical energy and a gas generation system for generating H2-rich gas for the current generation system.
Fuel cell systems for mobile applications use liquid fuel in order to generate hydrogen in the gas generation system. However, the gas generation system is only able to function after a certain operating temperature, which is dependent on the fuel, has been reached, and consequently it has to be heated up at the start of operation of the vehicle. The thermal energy required for this purpose is generated by burning fuel. In this case, the energy supply for the supply of air required for the combustion operation represents a limiting factor. The more air it is possible to provide for the combustion, the more quickly the operating temperature of the gas generation system is reached. Only after the operating temperature has been reached can the gas generation system supply fuel, for example hydrogen, for the fuel cells. However, electrical energy to drive the air-delivery device is required in order to supply air to the gas generation system. However, in mobile fuel cell systems, only a very limited amount of electric current is available before the operating temperature is reached and the fuel cell is started up.
In the prior art, these drawbacks are eliminated by using further storage units, e.g. a battery, a supercapacitor, or a hydrogen tank.
The following problems exist with the prior art:
an undesirable waiting time between the starting of the vehicle and driving off in the vehicle,
at low temperatures, a cold start is made even more difficult by the lack of power output from the battery,
the number of attempted starts without the battery having to be externally recharged is limited.
It is an object of the invention to provide a device which eliminates the problems of the prior art and is therefore able to improve the cold-starting performance of mobile fuel cell systems.
The following descriptive invention is described on the basis of a vehicle with a fuel cell system, although it is not restricted to mobile applications and is also advantageous for stationary applications.
According to the invention, there is an internal-combustion engine for generating mechanical energy, which can be connected to an air compressor for supplying air to the gas generation system via a drive shaft. Therefore, in the starting phase of the vehicle, the combustion air required for heating the gas generation system can be delivered without stored energy, e.g. without operating a battery. Consequently, the operating temperature of the gas generation system is reached more quickly, typically in less than 30 seconds, with the result that the starting time of the current generation system of the vehicle is reduced considerably. Current can only be provided by the current generation system when the operating temperature of the gas generation system is reached.
The output of the internal-combustion engine is advantageously in the range between 1 and 10 kW. The quantity of air delivered by the air compressor is advantageously up to 200 m3/h (s.t.p.), depending on the output of the internal-combustion engine.
There is advantageously a clutch, via which the internal-combustion engine can be connected to the air compressor. Therefore, if necessary the internal-combustion engine can be decoupled from the air compressor at any time and can be switched off, for example, in order to save fuel.
In a further advantageous embodiment, there is a mechanical device, for example a crank, or an electrical device, for example an onboard battery, for starting the internal-combustion engine. However, it is also possible for the internal-combustion engine to be started automatically by actuation of the door opener or the accelerator pedal of the vehicle or by the seat-belt being put on by the driver. Unnecessary waiting times until the operating temperature of the gas generation system is reached can thereby be avoided.
The cooling system of the internal-combustion engine is preferably connected to the cooling system of the vehicle.
The combustion exhaust gases of the internal-combustion engine are fed to a gas-cleaning system through an exhaust pipe and are discharged to the environment. The exhaust pipe of the internal-combustion engine is advantageously connected to the gas-cleaning system of the gas generation system. These measures lead to a more compact and lightweight structure of the vehicle.
In a particularly expedient embodiment, the internal-combustion engine is connected not only to the air compressor but also to a generator via the drive shaft. Therefore, the internal-combustion engine is able to supply both the air compressor and the generator with mechanical energy. The generator is able to supply not only the internal-combustion engine, via the onboard DC/DC converter, but also the 12 V network of the vehicle with current. The vehicle auxiliary units of the current generation system of the fuel cell system can also be powered via the 12 V network. Furthermore, the generator can charge the onboard battery for electrical cold-start ignition of the internal-combustion engine. Furthermore, the energy generated in the generator can be fed directly into the electric drive motor of the vehicle, with the result that the vehicle can be started in emergency situations, for example when the fuel cell system fails.
Furthermore, it is possible, depending on the operating state of the vehicle, for example when the vehicle is stationary, to connect up or decouple the internal-combustion engine. Therefore, for example when the vehicle is stationary, the current generation system can be switched off in order to save fuel. At the same time, the generator, which is driven by the internal-combustion engine, can be used to supply the vehicle auxiliary units, the internal-combustion engine and the fuel and water pumps with current.
In a further expedient embodiment of the invention, the generator can also be operated as an electric motor. It is therefore possible, when the internal-combustion engine is switched off and the clutch is closed, for the electric motor to drive the internal-combustion engine without ignition and fuel and therefore to use it as an additional air compressor.
Other advantages of the invention include:
that it allows a significantly smaller onboard battery to be used in the vehicle,
that the operating reliability is increased, since there is no restriction with regard to the number of attempted starts and with regard to the ability to start at low outside temperatures,
that the high-pressure compressor of the current generation system which is usually used is eliminated,
that in emergency situations the vehicle can be operated independently of the battery.